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Old 05-23-2019, 04:28 PM
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Factory Stock Heads and Intake

Hi,

I'm thinking of putting together a Factory Stock car for my dirt track next year. I'd like to start monitoring Craigslist to see if any useful parts come up.

The rules say:

The only GM head numbers allowed are 14079267, 3986336, 3986339, 986339X, 3986388, 3932441, 376445, 3928454, 3932454, 3876487, 3973487, 3973487X, 3973493, 3951598, 468642, 330862, 333882, 3998920, 3998991, 3998993, 3998997, and 3970126.

Which of these should I be on the lookout for? Which ones should I avoid?


Rules also say:

Stock OEM unaltered aluminum or cast iron intake only. No aftermarket or stock high performance or high rise.

It's a shame since I've been hanging onto a GM cast iron high rise marine intake for about 15 years. What intake part numbers (or car models) should I be looking for?


Thanks,
Sal

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Old 05-23-2019, 04:40 PM
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Need the rules on:
Compression
Fuel types
Carb size


Dont think of the engine power. Think of the power to the wheels.
What can you do within the rules to loose as little power from the cylinder to the tires?
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Old 05-23-2019, 04:56 PM
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Quote:
Originally Posted by cerial View Post
Need the rules on:
Compression
Fuel types
Carb size


Dont think of the engine power. Think of the power to the wheels.
What can you do within the rules to loose as little power from the cylinder to the tires?
Fuel is pump or racing gas. Maximum cranking compression 175lbs. Cast Holley 4412 -2 barrel only.

Cast piston only, must use 4 equal valve relief flattop or dish pistons. OEM crankshaft only- cannot belightened.

Hydraulic cam and flat tappet lifters only. .447 maximum lift at valve or .298 lobe lift at cam. Must maintain 14” of vacuum at 1200 rpm.

Stock unaltered cast iron exhaust manifolds only no porting or grinding allowed


Thanks!
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Old 05-23-2019, 06:38 PM
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My 1962 Chevrolet Bel Air has a 1968 350 CI engine equipped with a GM 3863151 single pattern camshaft with .447” valve lift and 222 degrees duration on intake and exhaust. That camshaft was used in 327 CI L-79 Engines. GM recommended at least 10:1 compression ratio with 10.5:1 to 11:1 compression ratio preferred when 100 octane gasoline was still available at the pump. The drive line should be a 4-speed manual transmission and 4.11:1 rear gears. That camshaft was discontinued by GM about 1995 but several aftermarket cam companies offer an exact duplicate. It works well with stock valve springs on double hump heads, a 4-Speed and 4.11:1 rear cogs. It was the cam to use in NHRA D/S class in the sixties. Shift points are from 5,300 to 5,500 rpm with Comp Cams 981-16 valve springs set up at 105 lb at 1.700” and 280 lb open pressure. Can use stock pressed in rocker studs with that spring pressure.

Last edited by MouseFink; 05-23-2019 at 06:48 PM.
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Old 05-23-2019, 07:15 PM
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Any cast iron or aluminum stock Quadra-Jet intake from 1967-1987, not any valuable difference in power between any of them....the aluminum just helps get weight off the nose of the car. Aluminum most commonly found on the HO 305 from 1978-87, and some 350's of that era.

The heads with an "X" after the casting number are supposed to have bigger runners, but with your rules package it really isn't going to matter.... a good race spec valve job is going to be a lot more valuable. Any of them with a 1.94" intake valve or bigger, avoid the 1.72" valve versions. The "882" tend to be very crack prone.

i'd contact a cam company or a custom cam grinder for a cam to maximize what you have within the lift and vacuum rules.
The 350HP 327 "151" cam Mousefink posted about won't be it, that is for sure. It has that lift, but won't even be close to right on lobe centerline, lobe separation , and cam duration.

The rules combination you have has been around for 30+ years now, there are no "magic bullets" on parts choices that are going to give anyone an clear advantage....that is why those rules are written the way they are.

It is going to be all the little blueprinting steps and touches that are going to make a winner, not any specific parts choices. 1 to 3 hp deals, as many as you can find to add up and give you a 15-25 hp advantage....you aren't going to find large 10Hp chunks from any part or modification...except maybe the valvejob. Ask around your area for the guy who is best at this, not every shop knows what to do...and it isn't just a "3-angle valvejob", there is more to it than that.

Chassis/handling tune and set-up is going to be far more important than anything you do in the engine bay, by far.
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Old 05-23-2019, 07:30 PM
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Awesome. Thanks for the help!
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Old 05-23-2019, 08:46 PM
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"Chassis/handling tune and set-up is going to be far more important than anything you do in the engine bay, by far."

You should make a large sign out of this and hang it over the door to the garage.
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Old 05-25-2019, 06:52 PM
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Well. Yea old rules which boxed you in.

Next step is to look at transmissions and stall options within the rules to see how low a stall and what gearing you can run to make the most out of that boat anchor
up front.

If they say must be stock th350 and 3.73 10 bolt but leave the converter options open use that.
If they leave the transmission options open well I would have a powerglide in there fast.
Even if they say use the th350 with factory converter but leave modifications to it open well there is things to make a th350 perform while staying in those rules.

Find power behind the engine. Then harness that power with handling.
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Old 05-25-2019, 08:54 PM
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As mentioned these rules don't have a lot of leeway in them. Camshaft refinement along the lines of a NHRA stocker grind is something to look into and I would be using a set of Rhoads lifters on it unless they are banned. What you're going to want more than anything is RPM so start figuring out what you can get by with to limit parasitic drag on the rotating assembly. Unless you have a cheap claimer rule in place I would be looking at coatings on everything possible. Assuming you're allowed at least a .030 cut on the cylinders, look for the thinest rings you can get by with and use a standard bore oil ring package to cut the drag. You'll be wanting a good block to, one that doesn't have a lot of core shift in it. On the intake, heads, etc - try to stick with upper level Corvette pieces. They tend to offer a few free HP when laid right next to their passenger car brothers. Also, see what you can do about getting that carb centered on the intake to try and equalize the cylinder filling as much as you can. You didn't say what they were holding you to on the ignition but some power can be found there too. Rocker arms are another place to look too. Make yourself a test fixture and measure them, keep the best ones but you might have to run through a a few dozen to find 16 good ones. Let the engine breathe too, vent the valve covers with at least 4 good sized breather elements. There are some tricks for adding additional fuel/air too.
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